It has always been an aim to produce an extruded plastic product which simulates wood with wood's warm aesthetic appearance but does not have the limitations of wood insofar as weathering, splitting, cracking, warping etc. To this end efforts have been made to print or laminate the surfaces of a plastic extrusion with patterns representing wood grains in an effort to give the plastic extrusion the appearance of wood. None of these methods has really been successful. These methods are currently in operation however require additional equipment(s) in order to print or laminate on to the surface combined with specialized equipment if the printing or laminating is done on an uneven surface. This secondary operation is often, depending on the profile, an operation which is done off-line, hence further increasing costs.
In other cases, materials have been mixed with the plastic material which is to be extruded in an effort to create the appearance of wood. U.S. Pat. No. 6,083,601, for example, is directed to providing a simulated wood product involving a complex processing system in which powdered cellulose, preferably sawdust, is mixed with a thermoplastic resin such as acrylonitrile butadiene styrene (ABS) or styrene acrylonitrile (SAN). The mixture is then compressed, heated and pelletized under carefully controlled conditions. These pellets are then used as a filler along with the thermoplastic resin in extruding a foamed core. This core is then covered by a clear coextruded protective cladding.
The requirement of having to use sawdust or the like as well as the complexity of the process renders the production of this simulated product costly and with the clear plastic covering the appearance and feel of the product lacks realism.
In another approach, Canadian Patent 2,399,354 discloses an extruded wood imitation component comprising an extruded body or core containing a mix of different colored thermoplastic polymer material which coloured material is said to produce veins of irregular lengths and shapes throughout the core and outer surfaces of the core to simulate natural wood. To improve the appearance of the component, it is said that wood particles may be mixed with the polymer material with the wood products making up from 3% to 40% of the core material. The process, according to this patent, is said to require careful control not only over the raw material but the equipment design and also the process conditions to produce the imitation wood product.
It is the object of this invention to provide a process for producing plastic extrusions which are made to have the appearance of a different selected one of a variety of different woods and which so simulate the variety of wood selected that it is essentially indistinguishable from that wood. It is a further object to provide such wood simulated plastic extrusions which are produced at a relatively low cost with a unique process utilizing unique equipment.